1. Field of the Invention
The present invention relates to a diffusion furnace and, more particularly, pertains to a microprocessor controlled vertically oriented thermal processor, also known as a diffusion furnace, for the processing of silicon or gallium arsenide wafers or substrates where vertically positionable furnace and process tube elements coaxially position, forming a double bell jar like contaminant free processing chamber.
2. Description of the Prior Art
The prior art diffusion furnaces have been horizontally oriented where uniform and quality products where influenced by variable factors including time, temperature, temperature ramp up rates, cool down rates, density of load, the size of the wafer, gas flow and concentration and temperature levels within the process chamber. Horizontal furnaces were not readily capable of high pressure oxidation or silicon deposition without special design, and often would not produce the quality levels desired. If high quality was attainable, the range of applications for the device was somewhat limited.
Prior art vertical furnaces were hindered by excessive process cool-down times, excessive maintenance, inaccessability of parts, particulate contamination, and other numerous reasons.
The present invention overcomes the disadvantages of the prior art by providing a microprocessor controlled vertical thermal processor including a double bell jar like assembly incorporated in a furnace with a vertically positionable furnace with an internal bell jar or element tube placed coaxially over another vertically positionable bell jar or process tube.